Question: The equation of a circle $C$ is $x^2+y^2+18x+32 = 0$. What is its center $(h, k)$ and its radius $r$ ?
Explanation: To find the equation in standard form, complete the square. $(x^2+18x) + (y^2) = -32$ $(x^2+18x+81) + (y^2) = -32 + 81 + 0$ $(x+9)^{2} + y^2 = 49 = 7^2$ Thus, $(h, k) = (-9, 0)$ and $r = 7$.